The present invention relates generally to compressors, including those used in refrigeration and HVAC applications. More particularly, the present invention relates to a pressure equalization system and method for starting a compressor, such as a scroll, rotary, or reciprocating compressor, while maintaining the condenser at high pressure.
A standard refrigeration or HVAC system includes a fluid, an evaporator, a compressor, a condenser, and an expansion valve. In a typical refrigeration cycle, the fluid begins in a liquid state under low pressure. The evaporator evaporates the low pressure liquid, which lowers the ambient temperature, and the liquid becomes a low pressure vapor. The compressor draws the vapor in and compresses it, producing a high pressure vapor. The compressor then passes the high pressure vapor to the condenser. The condenser condenses the high pressure vapor, generating a high pressure liquid. The cycle is completed when the expansion valve expands the high pressure liquid, resulting in a low pressure liquid. By means of example only, the fluid might be ammonia, ethyl chloride, Freon, or other known refrigerants.
Typically, upon start up of a compressor, the pressure at both the suction and the discharge of the compressor is low. In operation, the compressor works the fluid to achieve a high pressure at the discharge. However, when the compressor is no longer compressing fluid, the fluid on the high pressure side of the compressor (toward the condenser) flows back toward or to the low side of the compressor (toward the evaporator) until a state of equilibrium between the formerly high and formerly low pressure sides is achieved. Thus, the high pressure side equalizes with the low pressure side when the compressor stops operating. Such a system is inefficient because the refrigeration cycle requires energy at start up to create a high pressure in the condenser, which is needed to condense the fluid.
Another problem, specific to HVAC systems, is that it is difficult to efficiently achieve the high pressure start up necessitated by seasonal energy efficiency requirements (SEER), a system used to rate HVAC systems. Start up components, such as a start capacitor and a start relay, are commonly used to overcome the differential pressure when the compressor needs to start with the unbalanced pressure in the system. These components achieve a high pressure differential start when the system is turned on. These components are rather expensive, however, and they produce high voltages and currents in the compressor motor upon start up.
In light of the foregoing, there is a need for an improved system and method for equalizing the pressure for starting a compressor under high pressure loading.
Accordingly, the present invention is directed to an improved system and a method for starting a compressor while maintaining the compressor at a high pressure.
As explained in more detail below, the system and method of the present invention maintain a high pressure from a valve forward to a condenser, but allow the pressure below the valve to leak back toward the compressor suction until the pressure below the valve has equalized with the low pressure side of the compressor. By high loading the pressure above the valve and equalizing the pressure below the valve, expensive and potentially dangerous start up components are eliminated. A benefit specific to HVAC systems is that the SEER rating of the system is not sacrificed.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention is directed to a pressure equalization system for a compressor. The compressor has a compressor inlet for receiving a fluid at a first pressure from the evaporator and a compressor outlet for discharging the fluid at a second pressure to the condenser. The compressor is operable to compress the fluid from the first pressure to the second pressure. The system of the present invention includes a valve proximate to and in fluid communication with the compressor outlet and a bleed port upstream of the valve and in relatively low flow fluid communication with the compressor inlet. The valve has an open and a closed position. The valve is movable to the open position when the compressor is operating, to allow the fluid at the second pressure to flow through the valve. The valve is movable to the closed position when the compressor stops operating, to prevent backflow of the fluid at the second pressure through the valve toward the compressor inlet. The bleed port equalizes the pressure of the fluid contained in the compressor when the compressor stops operating.
In another aspect, the invention is directed to a pressure equalization system for a compressor having a high pressure side and a low pressure side, a compressor inlet for receiving a fluid at a first pressure, and a compressor outlet for discharging the fluid at a second pressure. The compressor is operable to compress the fluid from the first pressure to the second pressure. The system in this embodiment includes a container in fluid communication with the compressor, at least one valve operably disposed within the container, and a bleed port. The container has an inlet and an outlet, and either the inlet or the outlet of the container is connected to the outlet of the compressor. The container is divided into at least a first portion from the container inlet to the at least one valve and a second portion from the at least one valve to the container outlet. The valve is operably configured to allow the compressed fluid to flow through to the second portion of the container when the compressor is operating, and to prevent the compressed fluid in the second portion of the container from flowing back through the valve to the first portion of the container when the compressor stops operating. The bleed port connects the first portion of the container and the low pressure side of the compressor and is operably configured to bleed the compressed fluid from the first portion of the container to the low pressure side of the compressor when the compressor stops operating. The bleed port is further configured so that when the compressor is operating, the flow through the bleed port is relatively low, if not nonexistent. As a result, a negligible amount of fluid flows back to the compressor inlet when the compressor is operating.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed.